Numerous attempts have been made to rapidly form foam materials into sheets which are homogeneous while possessing structural strength and also retaining the cushioning effect of the foam. For example, "one-shot" procedures for rapidly building up a sheet of polyurethane foam using spray techniques are well known. For many applications it is desirable to incorporate fibers into the polymer mixture.
In U.S. Pat. No. 4,110,508 referred to above a procedure for incorporating fibers is described. In this application hydrophilic polyurethane prepolymer is foamed and the resulting foam is shredded. Subsequently the shredded foam is dispersed in combination with fibers (e.g. asbestos or wood pulp) into water and the resulting aqueous dispersion is wet-layered onto a support which can be a screen or fabric web.
The present invention is an alternate and superior method for preparing the sheets and sheet/fabric laminates described in U.S. Pat. No. 4,110,508, said application being expressly incorporated by reference into the present application to the extent U.S. Pat. No. 4,110,508 describes the urethane prepolymer employed, the method of foaming and shredding the foam to produce hydrophilic particles, the preparation of sheets and laminates and describes these products and their utilities.
The present invention is an improvement over the invention of U.S. Pat. No. 4,110,508 in that the separate steps of foaming and shredding the resulting foam are avoided. By use of the present invention a hydrophilic urethane prepolymer is dispersed in water and foamed simultaneously which results in a simplified process as well as a savings in time. Also it is possible to add the prepolymer directly to an aqueous dispersion of fibers to form a sheet having improved homogeneity. In this instance, sheets having improved tensile strength can be obtained.